1. Field
The present disclosure relates generally to detecting inconsistencies in structures and, in particular, to detecting inconsistencies in structures using waves transmitted through the structures.
2. Background
Composite and metallic aircraft structures may be susceptible to internal changes that may occur from different events. These events may include fatigue, impacts, mechanical stresses, electromagnetic effects, and other changes. These changes may occur suddenly or may occur over time. In some cases, these changes may be undesirable. Undesirable changes in aircraft structures are referred to as inconsistencies.
An aircraft may be inspected to determine whether inconsistencies have developed in structures in the aircraft. These inspections may be performed periodically or after visual indications reveal that inconsistencies may be present. Inconsistencies may occur from operations such as cargo loading and unloading. Other inconsistencies may occur through an unintended contact of a vehicle with an aircraft.
Inspections of the aircraft are time consuming and costly. These inspections reduce the time that an aircraft is available for flights. As a result, losses in revenue may occur when an aircraft is out of service for inspection.
The time that an aircraft is out of service may be reduced through the use of health monitoring systems. Health monitoring systems may be used to determine whether changes have occurred to structures in the aircraft without requiring the aircraft to be taken out of service. By having health monitoring systems built into, or associated with, the structures in an aircraft, these systems may monitor the structures during operation of the aircraft.
Health monitoring systems may employ ultrasonic testing. Ultrasonic testing involves using transducers to scan a structure in the aircraft. These transducers may function as transmitters and sensors. These transducers may be mounted on the surface of a structure or embedded in the structure. Transducers functioning as transmitters may generate waves that propagate into the structure. Transducers functioning as sensors detect the waves transmitted into the structure by the transmitters.
Typically, these detected waves are analyzed by the health monitoring system to determine whether inconsistencies may be present. A response signal generated in response to detecting waves propagating through a structure may be compared to signals for a baseline for the structures. The signals for the baseline are generated when the structures in the aircraft do not have inconsistencies. The comparison of the response signal with the signals for the baseline is used to determine whether inconsistencies may be present.
Structures, however, may change over time even though inconsistencies that are undesirable may not be present. As a result, comparison between response signals and baseline signals may not be as effective because, over time, the baseline may become more and more different from response signals generated by the health monitoring system.
As a result, a health monitoring system may indicate a presence of an inconsistency even though one is not present. A new baseline may need to be generated for the structure. Generating a new baseline for the structure may be time-consuming. Additionally, in generating a new baseline, additional time and expense may be needed to perform other testing to ensure that inconsistencies are not present in the structures for which the new baseline is created.
Therefore, it would be desirable to have a method and apparatus that takes into account at least some of the issues discussed above as well as possibly other issues.